NEW ORLEANS (AP) — Democratic Rep. Charlie Melancon, a self-styled centrist ‘‘Blue Dog’’ Democrat, said Thursday that he will run for Senate next year against incumbent David Vitter, the conservative Republican whose family-values image took a hit in a 2007 prostitution scandal.

Melancon’s announcement had been anticipated. Vitter’s campaign has been attacking him in Internet ads and videos as a liberal ally of President Barack Obama.

Touting himself as an anti-abortion, pro-gun businessman, Melancon didn’t mention the prostitution scandal in his announcement but said ‘‘Louisiana deserves better’’ than Vitter. ‘‘Louisiana needs a different approach. More bipartisan. More disciplined. More honest and with a whole lot more commonsense,’’ he said.

‘‘I welcome Charlie to the race and look forward to an important, spirited debate,’’ Vitter said in a prepared statement.

Melancon’s announcement comes amid the national health care debate. Vitter opposes Democratic plans to overhaul the health care system, including the ‘‘public option’’ that would let a government program compete with private insurers.

Citing votes Melancon cast on amendments in a House committee, the Vitter camp and state Republicans say Melancon is for Obama-backed, government-run health care.

‘‘I voted against the health care bill, that’s the bottom line,’’ Melancon said Thursday. He said he is concerned about the bill’s cost, its lack of an explicit prohibition on abortion funding and the public option. He said a compromise is possible, ‘‘but only if people are talking to each other’’ in Congress.

Melancon, of Napoleonville, is the only Democrat in Louisiana’s House delegation. He is serving his third term. Melancon’s district includes much of the state’s marshy coast, part of Cajun country and a stretch along the Mississippi River between New Orleans and Baton Rouge.

Vitter won a House seat representing suburban New Orleans in 1999 after the resignation of Rep. Robert Livingston. He became the state’s first Republican senator since Reconstruction when he was elected to the seat vacated by the retiring Democrat John Breaux in 2004.

Vitter built a conservative record with votes against raising the minimum wage, tough stances against illegal immigration, support of Iraq policy during the administration of President George W. Bush and opposition to abortion and same-sex marriage. His national profile was rising until his number surfaced in phone records of a Washington prostitution ring.

Vitter admitted to an unspecified ‘‘serious sin’’ and denied allegations of relationships with prostitutes in New Orleans. He kept a low profile until emerging in late 2008 as a staunch critic of government business bailouts and later of Obama’s fiscal stimulus package and health care proposals.

Asked if he will make the scandal an issue, Melancon said he intends to run a positive campaign stressing his background and accomplishments. But he added, ‘‘I think the people are going to want to know a lot more’’ about the scandal.

Elliott Stonecipher, a Shreveport political consultant and demographer, said Vitter remains strong. Melancon, he said, faces a tough campaign in a state where Obama policies are unpopular and voting trends have favored Republicans. Stonecipher and University of New Orleans political science professor Ed Chervenak both noted that Melancon’s decision to enter the race may stem from expectations Louisiana will lose a House seat after the 2010 census, and redistricting would make his re-election unlikely.

‘‘Vitter is running for his political life. Charlie Melancon’s running because it’s the best thing that’s available right now,’’ Stonecipher said.

Melancon denied that scenario. ‘‘I’ve been trying to find a Republican or a Democrat for over a year to run against this guy,’’ he said. ‘‘Nobody has stepped up.’’

Melancon’s vote for Obama’s stimulus package and early support for a measure that would allow employees to form a union by signing cards instead of by secret ballot have fueled Republican campaign rhetoric.

‘‘Voters in Louisiana aren’t looking to send a rubber stamp for Obama’s agenda to the U.S. Senate,’’ state GOP chairman Roger Villere said.

Melancon, however, has broken with Obama on health care and other issues. He voted against the so-called ‘‘cap and trade’’ climate bill, saying it would hurt Louisiana’s oil-and-gas economy.

And he has said he wants to find compromise on the union-backed legislation, saying he wants to preserve the secret ballot.

Melancon is the only Democrat so far to publicly challenge Vitter.

Robert Lang, 64, a political unknown from Natchitoches, has said he will run as an independent. Stormy Daniels, an adult movie actress from Baton Rouge now living in Florida, has formed an exploratory committee, insisting she is seriously considering the race.

Other potential challengers may be discouraged by the campaign funds built by Vitter — more than $3 million — and Melancon, who has more than $1 million.